Conventional two-way radio systems operating in the duplex mode require two different frequencies for communication in two directions to take place simultaneously. However, this wastes spectrum. The main attraction for any full-duplex two-way radio system is the ability for the listener to interrupt and speak at any time. An approach, illustrated in U.S. Pat. No. 4,037,158, and assigned to the same assignee as the instant application, is to provide simulated duplex operation on a single channel, utilizing hardware control of the transmitter and receiver by sampling the channel for the presence of a carrier wave. This approach generally requires increased radio complexity.
Time division multiplexing (TDM) of voice and data onto a single channel is known to provide full-duplex radio operation. Typically, however, this requires at least two time slots for a radio to transmit half the time and to receive at half the time. While effective, this practice wastes spectrum since, in ordinary conversations, the talker usually receives only brief feedback responses (or acknowledgements) during his or her transmissions.